When fertilization occurs within mammals, the sex is immediately determined. Each parent will contribute one or more chromosomes during the fertilization process, depending on the species. In the male heterogametic (XY) system, the absence of the Y chromosome results in a female offspring and the presence of the Y chromosome results in a male. The evolution of the sex determination system consists of the rise and development of sex chromosomes and concurrently the emergence and evolution of genes that guarantee the formation of equivalent traits and functions. This paper will examine three studies: the replication of Y chromosomes and how they have evolved overtime (Cortez et al. 2014), the structural variation found in Y chromosomes…show more content… 2014).
The purpose of the experiment was to understand how reproductive cells can divide and reproduce and what is being reproduced in the duplication process. This process will assist researchers in understanding the role of the Y chromosome and its evolution over time. An experiment was conducted where RNA-sequence data for 166 tissue samples from nine mammals and two birds were observed (Cortez et al. 2014). Cortez et al. (2014) sequenced genomic DNA from two individuals and then assembled the Y and W linked transcripts. Next, the Y/W transcripts were validated by aligning the male and female Illumina genomic readings. In order to validate this, a large-scale subtraction approach was used. Next, Cortez et al. (2014) reconstructed the Y-linked genes using genomic data and then defined the Y gene names and the X gametologues. Experimenters predicted the multi-copy genes and the characterization of x-linked contigs and genes in platypus. A phylogenetic analysis was used to align the coding sequences for phylogenetic tree reconstructions based on amino acid sequences. All trees were inspected for evidence of gene conversion but could not find any. Thus, it is not frequent in the evolution of sex chromosomes (Cortez et al. 2014). Cortez et al. (2014) have concluded that the XY system is not only unique to males, but similar to the ZW system found in female birds.